Semisynthesis of Intact Complex-Type Triantennary Oligosaccharides from a Biantennary Oligosaccharide Isolated from a Natural Source by Selective Chemical and Enzymatic Glycosylation

Abstract

Attachment of oligosaccharides to proteins is a major post-translational modification. Chemical syntheses of oligosaccharides have contributed to clarifying the functions of these oligosaccharides. However, syntheses of oligosaccharide-linked proteins are still challenging because of their inherent complicated structures, including diverse di- to tetra-antennary forms. We report a highly efficient strategy to access the representative two types of triantennary oligosaccharides through only 9- or 10-step chemical conversions from a biantennary oligosaccharide, which can be isolated in exceptionally homogeneous form from egg yolk. Four benzylidene acetals were successfully introduced to the terminal two galactosides and two core mannosides of the biantennary asialononasaccharide bearing 24 hydroxy groups, followed by protection of the remaining hydroxy groups with acetyl groups. Selective removal of one of the benzylidene acetals gave two types of suitably protected glycosyl acceptors. Glycosylation toward the individual acceptors with protected Gal-β-1,4-GlcN thioglycoside and subsequent deprotection steps successfully yielded two types of complex-type triantennary oligosaccharides.

A Study for the Access to a Semi-synthetic Regioisomer of Natural Fucosylated Chondroitin Sulfate with Fucosyl Branches on N-acetyl-Galactosamine Units

“…In the first one a concentrated aqueous solution of acetic acid was employed (90% w/w acetic acid in water, resulting in a solution with a protic activity approximately equal to that of reaction c in Figure 2). Under similar conditions, the selective cleavage of 4,6-O-benzylidene rings on complex N-glycan oligosaccharide derivatives [41] and then, during the development of this work, also on chondroitin oligosaccharide derivatives [42] have been reported. In the second reaction, 2 was treated with an organic Brønsted acid such as (+)-camphor-10-sulfonic acid (CSA) in acetonitrile (ACN) in the presence of an acetal exchange reagent (1,4-dithiothreitol, DTT).…”

Identification of the binding roles of terminal and internal glycan epitopes using enzymatically synthesized N-glycans containing tandem epitopes

“…33,35 For some of the core glycans which are readily available from an abundant natural source, purification followed by additional processing such as trimming using exoglycosidases or acid hydrolysis 36–38 is a good alternative. We name the strategy Core Isolation/Enzymatic Extension (CIEE) and use it for the desired biantennary N -glycans.…”

An enzymatic strategy to asymmetrically branched N-glycans

“…8 And due to the diversity and complexity, as well as low abundance of most structures, it is extremely challenging to isolate adequate amounts of N -glycans with specific structures from natural sources. On the other hand, despite numerous efforts on chemical synthesis of N -glycans, 9 only a few groups had recently developed strategies for synthesizing libraries of structurally defined N -glycans, including Boons’s general strategy for chemoenzymatic synthesis of asymmetric N -glycans, 6, 10 Wong’s modular synthesis of HIV N -glycans, 11 and our core synthesis/enzymatic extension (CSEE) strategy to prepare N -glycan isomers. 12 Nevertheless, all strategies require expertise and proficient skills for chemical synthesis of key asymmetric N -glycan core or modular structures for further enzymatic diversification.…”